1. Field of the Invention
The present invention relates to an angular velocity sensor for measuring an angular velocity by using a piezoelectric oscillation type gyro, and this sensor is used for measuring the moving state of a moving body such as a vehicle, ship, airplane or robot.
2. Related Arts
There is known an oscillation type angular velocity sensor using piezoelectric elements (as disclosed in Japanese Patent Application Laid-Open No. 61-191917 or 62-19714, for example). In this oscillation type angular velocity sensor, as shown in FIG. 19, driving piezoelectric elements 33 and 34 and detecting piezoelectric elements 35 and 36 are perpendicularly arranged because Coriolis force to be generated in the direction perpendicular to the driven oscillating direction has to be detected. Specifically, in the typical oscillation type angular velocity sensor having the piezoelectric elements adhered to a metallic oscillator 37, the driving piezoelectric elements 33 and 34 and the detecting piezoelectric elements 35 and 36 are arranged on the orthogonal planes to make a stereoscopic structure.
However, this structure has a problem that its manufacturing process is required to have steps of adhering the individual piezoelectric elements to different faces of the oscillator, so that the manufacturing process becomes complicated. Further, according to this structure, a size of the angular velocity sensor becomes large.
In Japanese Patent Application Laid-Open No. Hei 6-147903, there has been proposed an angular velocity sensor in which a silicon substrate is etched from its two faces to form an integral oscillator in the substrate and in which driving or detecting piezoelectric thin films are laminated on the surfaces of the oscillator. According to this construction, the oscillator, the drive unit, the detection unit and the peripheral circuits are integrated on the substrate so that a small angular velocity sensor can be achieved.
However, this angular velocity sensor has problems that the drive signal to be applied for operating the sensor to the drive unit is caused to flow around the wiring line of feedback elements or detection elements by the induction or the electrostatic capacity coupling to cause noises, thereby making the drive signal unstable or to deteriorate the detection accuracy of the sensor. Especially, the angular velocity sensor, in which the oscillator is formed by etching the silicon substrate, is seriously influenced by the signal flow-around because it is small-sized to have its individual units close to each other.
As the method for reducing the signal flow-around, there is disclosed in Japanese Patent Application Laid-Open No. Hei. 3-131713, for example, an angular velocity sensor which is constructed such that the capacity coupling between the individual wiring lines of the drive unit and the detection unit are interrupted. Specifically, there is arranged in a terminal insulating portion, in which driving terminals and detecting terminals are buried, an earth plate for isolating the driving terminals and the detecting terminals. At the same time, a portion of the earth plate is exposed from the terminal insulating portion to the outside so that the exposed portion of the earth plate is arranged between the wiring lines of the individual terminals, and the sections of the sensor, as not reached by the earth plate, are electrostatically shielded by grounding the metallic oscillation plate, which is arranged between the two terminals, to the earth.
By this method, however, the shield is not complete and so the signal flow-around cannot be completely prevented, whereby it is difficult to eliminate the noises.